弱い摂動が誘発する有機半導体の電子機能：有機デバイス関連界面のミステリーの解明

2013 Fiscal Year Annual Research Report

• Project/Area Number: 24245034
• Research Institution: Chiba University
• Principal Investigator: 上野 信雄 千葉大学, 融合科学研究科(研究院), 教授 (40111413)
• Project Period (FY): 2012-04-01 – 2015-03-31
• Keywords: 有機半導体 / 有機デバイス / 界面 / エネルギー準位接合 / 移動度 / 光電子分光 / 電子状態 / 電子-振動結合

Research Abstract

光電子分光法は、物質中の電子エネルギー分布を直接測定できる最も有力な手法であるが、有機材料の測定ではイオン化に使用する光による照射損傷のため高感度測定は不可能と言われていた。昨年度までの研究でUPS装置の改良によって歴史的に初めてとなる5E16states/cm3eVの電子状態検出を実現した。これによって、特に弱い相互作用で形成される有機デバイス関連界面で生じる様々な現象の実験結果に基づいた電子論的解明を実現し、有機結晶に共通する界面電子準位接続機構を正しく論ずることが可能になった。H25年度の研究において、ペンタセン薄膜中のホールトラップ（バンドギャップ中の占有電子準位）のエネルギー分布の測定結果を確定し、この主要な原因がいわゆる不純物によるものではなく分子集合構造の乱れによるものであり、膜の1気圧の窒素ガスへの暴露によって出現することを突き止めた。同様の結果がArガス暴露によって得られ、さらにペンタセン薄膜の結晶グレインサイズが大きい場合には窒素ガスに暴露しても変化しないことが分かった。すなわち、薄膜中の微結晶境界の構造乱れからガス分子/原子が結晶中に拡散し構造不完全性が増加することが分かった。この結果、フェルミ準位の変動によって界面エネルギー準位接続が変化し，同時に電荷トラップが増加する。関連して、非占有準位の研究も行った。一方、この結果は、高機能の有機薄膜デバイスの製造には、窒素ガス中でのデバイスの製造過程そのものを見直す必要があることを指摘している。
超高感度UPSによって多様な有機半導体薄膜・単結晶の本来の電子状態の研究が可能となった。上記の研究に関連して、X線散乱による精密な構造解析も実施することによって、有機/有機pn接合界面においても分子集合構造の不完全性と界面電子準位接続に顕著な相関があることを見出し、これがバンドギャップ状態間の電子移動に起因することを定量的に測定しつつある。

Current Status of Research Progress

1: Research has progressed more than it was originally planned.

Reason

当初予定の計画を概ね完了し，さらに発展的な研究を行うことができた。またこの過程で本研究の目的に関連して新しい課題や可能性を見出しその研究の第一歩となる実験に着手できた。また、バンドギャップ中の電子準位制御を、海外の研究グループと協力して実デバイス作製に応用し、デバイス性能が飛躍的に改善される見通しも得た。これらの結果、最終年度で実施すべき計画も明確になった。

Strategy for Future Research Activity

H25年度までの研究成果を踏まえ研究を進展させる。第一に、有機/有機ヘテロ接合界面における分子集合構造の不完全性、界面電子準位接続とバンドギャップ状態間の電子移動の関連性を直接的に測定する。第二に、より弱い分子間相互作用が、分子集合構造や電子状態に及ぼす影響を研究する。平面構造を持つ分子の端に存在する>C-Hを介した分子間水素結合、C-Hσ結合による影響も無視できないことが浮上しているため、二種類の異なる分子を不活性基板表面上に平らに二次元的に配列させた系（DIPとフッ化ペンタセンなど）を活用してその影響についても探査する。第三に、昨年度までの研究から、電子-格子相互作用の影響を精密に測定できるようになったため、有機単結晶（ルブレン）のスモールポーラロン（ホール伝導に大きく関わる准粒子）のバンド分散への効果を測定する。
以上から、弱い分子間相互作用などを特徴とする有機半導体に普遍的な性質について総合的に考察し、特に多様な有機デバイスの性能に影響を及ぼす界面エネルギー準位接合機構の原因を解明して、新しい接合モデルを提案する。

Research Products

• [Journal Article] Seleno groups control the energy-level alignment between conjugated organic molecules and metals (2014)
  • Author(s): J. Niederhausen, S. Duhm, G. Heimel, C. Buerker, Q. Xin, A. Wilke, A. Vollmer, F. Schreiber, S. Kera, J. P. Rabe, N. Ueno, and N. Koch
  • Journal Title: J. Chem. Phys. Volume: 140 Pages: 014705-1-12
  • DOI: 10.1063/1.4858856
  • Peer Reviewed
• [Journal Article] Energy level realignment in weakly interacting donor-acceptor binary molecular networks (2014)
  • Author(s): J-Q. Zhong, X. Qin, J-L. Zhang, S. Kera, N. Ueno, A. T. S. Wee, J. Yang, and W. Chen
  • Journal Title: ACS Nano Volume: 8 Pages: 1699-1707
  • DOI: 10.1021/nn406050e
  • Peer Reviewed
• [Journal Article] Charged and metallic molecular monolayers through surface-induced aromatic stabilisation (2013)
  • Author(s): G. Heimel, S. Duhm, I. Salzmann, A. Gerlach, A. Strozecka, J. Niederhausen, C. Buerker, T. Hosokai, I. Fernandez-Torrente, G. Schulze, S. Winkler, A. Wilke, R. Schlesinger, J. Frisch, B. Brueker, A. Vollmer, B. Detlefs, J. Pflaum, S. Kera, K. J. Franke, N. Ueno, J. I. Pascual, F. Schreiber, and N. Koch,
  • Journal Title: Nature Chem. Volume: 5 Pages: 187-194
  • DOI: 10.1038/nchem.1572
  • Peer Reviewed
• [Journal Article] Impact of molecule-dipole orientation on energy level alignment at the submolecular scale (2013)
  • Author(s): Y. L. Huang, W. Chen, F. Bussolotti, T. C. Niu, A. T. S. Wee, N. Ueno, and S. Kera
  • Journal Title: Phys. Rev. B Volume: 87 Pages: 085205-1-6
  • DOI: 10.1103/PhysRevB.87.085205
  • Peer Reviewed
• [Journal Article] Recoil effects in valence bands photoemission of organic solids (2013)
  • Author(s): M. Shang, T. Fujikawa, and N. Ueno
  • Journal Title: Anal. Chem. Volume: 85 Pages: 3739-3745
  • DOI: 10.1021/ac4000865
  • Peer Reviewed
• [Journal Article] Inverted polymer solar cells integrated with small molecular electron collection layer (2013)
  • Author(s): A. Shi, Y. Li, Z. Xu, F. Sun, J. Li, X. Shi, H. Wei, S. Lee, S. Kera, N. Ueno, and J. Tang
  • Journal Title: Organic Electronics Volume: 14 Pages: 1844-1851
  • DOI: 10.1016/j.orgel.2013.04.029
  • Peer Reviewed
• [Journal Article] Gap states in pentacene thin film induced by inert gas exposure (2013)
  • Author(s): F. Bussolotti, S. Kera, K. Kudo, A. Kahn and N. Ueno
  • Journal Title: Phys. Rev. Lett. Volume: 110 Pages: 267602-1-5
  • DOI: 10.1103/PhysRevLett.110.267602
  • Peer Reviewed
• [Journal Article] Experimental reorganization energies of pentacene and perfluoropentacene: Effects of perfluorination (2013)
  • Author(s): S. Kera, S. Hosoumi, K. Sato, H. Fukagawa, S. Nagamatsu, Y. Sakamoto, T. Suzuki, H. Huang, W. Chen, A. T. S. Wee, V. Coropceanu, and N. Ueno
  • Journal Title: J. Phys. Chem. C Volume: 117 Pages: 22428-22437
  • DOI: 10.1021/jp4032089
  • Peer Reviewed
• [Journal Article] Electron affinity of pentacene thin film studied by radiation-damage free inverse photoemission spectroscopy (2013)
  • Author(s): W. N. Han, H. Yoshida, N. Ueno, and S. Kera
  • Journal Title: Appl. Phys. Lett. Volume: 103 Pages: 123303-1-5
  • DOI: 10.1063/1.4821445
  • Peer Reviewed
• [Journal Article] Pentacene on Ag(111): Correlation of bonding distance with intermolecular interaction and order (2013)
  • Author(s): S. Duhm, C. Buerker, J. Niederhausen, I. Salzmann, T. Hosokai, J. Duvernay, S. Kera, F. Schreiber, N. Koch, N. Ueno, and A. Gerlach
  • Journal Title: ACS Appl. Mater. Interfaces Volume: 5 Pages: 9377-9381
  • DOI: 10.1021/am402778u
  • Peer Reviewed
• [Journal Article] Quantitatively identical orientation-dependent ionization energy and electron affinity of diindenoperylene (2013)
  • Author(s): W. N. Han, K. Yonezawa, R. Makino, K. Kato, A. Hiderhofer, R. Murdey, R. Shiroishi, H. Yoshida, N. Sato, N. Ueno, and S. Kera
  • Journal Title: Appl. Phys. Lett. Volume: 103 Pages: 253301-1-4
  • DOI: 10.1063/1.4850531
  • Peer Reviewed
• [Presentation] Structural requirement on the surface-induced aromatic stabilization (2013)
  • Author(s): T. Hosokai, K. Yonezawa, K. Kato, R. Makino, J. Yang, K. R. Koswattage, A. Gerlach, F. Schreiber, N. Ueno and S. Kera
  • Organizer: MRS fall meeting 2013
  • Place of Presentation: Boston, USA
  • Year and Date: 20131206-20131206
• [Presentation] The effect of molecular adsorption-geometry on the binding energy of interface states (2013)
  • Author(s): K. Kato, K. Sato, K.Yonezawa, Y. Liu, T. Hosokai, S. Yanagisawa, K. R. Koswattage, N. Ueno, S. Kera
  • Organizer: MRS fall meeting 2013
  • Place of Presentation: Boston, USA
  • Year and Date: 20131206-20131206
• [Presentation] Large impact of molecular orientation on ionization energy: picene film (2013)
  • Author(s): R. Makino, K. Yonezawa, K. Kato, A. Hinderhofer, T. Hosokai1, K. K. Okudaira, N. Ueno, and S. Kera
  • Organizer: MRS fall meeting 2013
  • Place of Presentation: Boston, USA
  • Year and Date: 20131206-20131206
• [Presentation] Band-gap states related to the nature of organic semiconductors controls the energy level alignment (2013)
  • Author(s): Nobuo Ueno
  • Organizer: Asian Pacific Conference on Chemistry of Materials (APCCOM2013)
  • Place of Presentation: City University of Hong Kong, Hong Kong
  • Year and Date: 20131203-20131206
  • Invited
• [Presentation] The nature of organic semiconductors: Universal origin of their peculiar electronic properties (2013)
  • Author(s): Nobuo Ueno
  • Organizer: The Kyoto JSAP-MRS joint meeting
  • Place of Presentation: Kyoto、Japan
  • Year and Date: 20130916-20130920
  • Invited
• [Presentation] Reinvestigation of the band-gap energy of pentacene thin film (2013)
  • Author(s): W. Han, H. Yoshida, N. Ueno, and S. Kera
  • Organizer: The Kyoto JSAP-MRS joint meeting
  • Place of Presentation: Kyoto, Japan
  • Year and Date: 20130916-20130920
• [Presentation] Impact of structural defects on the energy level alignment at organic-organic iintefaces (2013)
  • Author(s): K. Yonezawa, A. Hinderhofer, T. Hosokai, K. Kato, F. Schreiber, N. Ueno and S. Kera
  • Organizer: The Kyoto JSAP-MRS joint meeting
  • Place of Presentation: Kyoto, Japan
  • Year and Date: 20130916-20130920
• [Presentation] Impact of film structure on ionization energy of titanyl-phthalocyanine in thin film (2013)
  • Author(s): T. Hosokai, K. Yonezawa, T. Kanayama, T. Koganezawa, K.K. Okudaira, S. Kera and N. Ueno
  • Organizer: The Kyoto JSAP-MRS joint meeting
  • Place of Presentation: Kyoto, Japan
  • Year and Date: 20130916-20130920
• [Presentation] Molecular-orientation dependent ionization energy of picene films (2013)
  • Author(s): Rintaro Makino, Keiichirou Yonezawa, Kengo Kato, Alexander Hinderhofe, Takuya Hosokai, Koji K. Okudaira, Nobuo Ueno, Satoshi Kera
  • Organizer: The Kyoto JSAP-MRS joint meeting
  • Place of Presentation: Kyoto, Japan
  • Year and Date: 20130916-20130920
• [Presentation] Surface-induced aromatic stabilization of disc-like conjugated molecules (2013)
  • Author(s): Steffen Duhm, Benjamin Broker, Alexander Gerlach, Christoph Burker, Jens Niederhausen, Ingo Salzmann, Takuya Hosokai, Jorg Zegenhagen, Antje Vollmer, Ralph Rieger, Satoshi Kera, Klaus Mullen, Nobuo Ueno, Frank Schreiber and Norbert Koch
  • Organizer: The Kyoto JSAP-MRS joint meeting
  • Place of Presentation: Kyoto, Japan
  • Year and Date: 20130916-20130920
• [Presentation] A universal property of molecular crystals probed with ultrahigh-sensitivity photoelectron spectroscopy: Band-gap states appear by weak perturbation and control the energy level alignment (2013)
  • Author(s): Nobuo Ueno
  • Organizer: The 11th China-Japan Joint Symp. on Conduction and Photoconduction in Organic Solids and Related Phenomena
  • Place of Presentation: Changchun, China
  • Year and Date: 20130901-20130903
  • Invited
• [Presentation] Electron affinity of pentacene thin film studied by radiation-damage free inverse photoemission spectroscopy (2013)
  • Author(s): W. Han, H. Yoshida, N. Ueno, and S. Kera
  • Organizer: The 11th China-Japan Joint Symp. on Conduction and Photoconduction in Organic Solids and Related Phenomena
  • Place of Presentation: Changchun, China
  • Year and Date: 20130901-20130903
• [Presentation] Geometric and Electronic Structure of Templated C60 on DIP, the 11th China-Japan Joint Symposium on Conduction and Photoconduction in Organic Solids and Related Phenomena (2013)
  • Author(s): A. Hinderhofer, A. Gerlach, K. Broch, T. Hosokai, K. Yonezawa, K. Kato, J. Yang, Q. Sun, S. D. Wang, S. Kera, N. Ueno, F. Schreiber
  • Organizer: The 11th China-Japan Joint Symp. on Conduction and Photoconduction in Organic Solids and Related Phenomena
  • Place of Presentation: Changchun, China
  • Year and Date: 20130901-20130903
• [Presentation] Potassium doping of single crystalline pentacene thin film: Can pentacene become a Mott-Hubbard insulator? (2013)
  • Author(s): F. Bussolotti, S. Kera, N. Ueno
  • Organizer: The 38th international conference on vacuum ultraviolet and x-ray physics (VUVX2013)
  • Place of Presentation: Hefei, China
  • Year and Date: 20130712-20130719
• [Presentation] Electronic property and the nature of organic semiconductor (2013)
  • Author(s): Nobuo Ueno
  • Organizer: 14th International Conference on Formation of Semiconductor Interfaces (ICFSI-14)
  • Place of Presentation: Hyundai Hotel, Gyeongju, Korea
  • Year and Date: 20130630-20130704
  • Invited
• [Presentation] Gap states in pentacene produced by inert-gas exposure:Direct detection by ultrahigh-sensitivity UPS (2013)
  • Author(s): Fabio Bussolotti, Satoshi Kera, Kazuhiro Kudo, Antoine Kahn and Nobuo Ueno
  • Organizer: The 7th international workshop on "Electronic Structure and Processes at Molecular-Based Interfaces"(ESPMI-VII)
  • Place of Presentation: Weizmann Institute of Science, Rehovoth, Israel
  • Year and Date: 20130428-20130502
  • Invited
• [Presentation] A Novel Intermolecular Interaction Mediated by Intramolecular Polar Bonds at Organic Heterojunction (2013)
  • Author(s): K. Yonezawa, Jia-Lin Zhang, See Liang Wong, Tianchao Niu, Alexander Hinderhofer, Wei Chen, Nobuo Ueno, Satoshi Kera
  • Organizer: The 7th international workshop on "Electronic Structure and Processes at Molecular-Based Interfaces" (ESPMI-VII)
  • Place of Presentation: Weizmann Institute of Science, Rehovoth, Israel
  • Year and Date: 20130428-20130502
• [Presentation] Molybrenum Trioxide Doped C60: Charge Transfer State Studied by Ultraviolet Photoemission Spectroscopy (2013)
  • Author(s): JP. Yang, S. Kera, N. Ueno
  • Organizer: The 7th international workshop on "Electronic Structure and Processes at Molecular-Based Interfaces" (ESPMI-VII)
  • Place of Presentation: Weizmann Institute of Science, Rehovoth, Israel
  • Year and Date: 20130428-20130502
• [Presentation] Impact of structural order on the electronic level alignment of organic heterostructures (2013)
  • Author(s): A. Hinderhofer, K. Yonezawa, T. Hosokai, K. Kato, F. Schreiber, S. Kera, N. Ueno
  • Organizer: The 7th international workshop on "Electronic Structure and Processes at Molecular-Based Interfaces" (ESPMI-VII)
  • Place of Presentation: Weizmann Institute of Science, Rehovoth, Israel
  • Year and Date: 20130428-20130502
• [Presentation] Anisotropy of electron-phonon coupling for pentacene monolayer (2013)
  • Author(s): S. Kera , F. Bussolotti, and N. Ueno
  • Organizer: The 7th international workshop on "Electronic Structure and Processes at Molecular-Based Interfaces" (ESPMI-VII)
  • Place of Presentation: Weizmann Institute of Science, Rehovoth, Israel
  • Year and Date: 20130428-20130502
  • Invited